85 Io

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85 Io
Discovered byC. H. F. Peters
Discovery dateSeptember 19, 1865
Other namesA899 LA; A899 UA
CategoryMain belt
Reference date March 6, 2006 (JD 2453800.5)
Longest distance from the Sun473.341 Gm (3.164 AU)
Shortest distance from the Sun320.334 Gm (2.141 AU)
Longest distance from the center of its orbital path
("semi-major axis")
396.837 Gm (2.652 AU)
How long it takes to complete an orbit1578.081 d (4.32 a)
Average speed18.12 km/s
Mean anomaly206.947°
Angle above the reference plane
Size and other qualities
Measurements180×160×160 km[1][4]
Mass~3.4×1018 (estimate)
Average density~1.4 g/cm³ (estimate)[5]
Surface gravity~0.028 m/s² (estimate)
Escape velocity~0.07 km/s (estimate)
Rotation period0.2864 d (6.875 h) [2]
How much light it reflects0.067 [3]
Avg. surface temp.~172 K
max: 272K (-2° C)
Spectral typeC-type asteroid
True brightness
("absolute magnitude")

85 Io is a big, dark Main belt asteroid of the C spectral class. It is probably a primitive body made of carbonates. Like 70 Panopaea it orbits within the Eunomia asteroid family but it is not related to the shattered parent body.

Io is a retrograde rotator, with its pole pointing towards one of ecliptic coordinates (β, λ) = (-45°, 105°) or (-15°, 295°) with a 10° uncertainty[1]. This gives an axial tilt of about 125° or 115°, respectively. Its shape is quite spherical.

It was found by C. H. F. Peters on September 19, 1865 and named after Io, a lover of Zeus in Greek mythology.

A diameter of 178 kilometres was measured from an occultation of a star on December 10, 1995 [4].

Io is also the name of the volcanic moon of Jupiter. With a two-digit number and a two-letter name, 85 Io has the shortest designation of all minor planets.

Other websites[change | change source]

References[change | change source]

  1. PDS lightcurve data
  2. A. Erikson Photometric observations and modelling of the asteroid 85 Io in conjunction with data from an occultation event during the 1995-96 apparition, Planetary and Space Science, Vol. 47, p. 327 (1999).
  3. G. A. Krasinsky et al. Hidden Mass in the Asteroid Belt, Icarus, Vol. 158, p. 98 (2002).